# CVE-2026-59851: Libssh: libssh: authentication bypass via missing gssapi principal check

Status: published. Published: 2026-07-21. Updated: 2026-11-04.

A flaw was found in libssh. On servers with GSSAPIKeyExchange enabled, the gssapi-keyex path does not verify whether the authenticated Kerberos principal is authorized for the requested local user, allowing authenticated clients to log in as arbitrary users.

## Remediation

- workaround: Disable GSSAPIKeyExchange. (source: CNA: redhat)

## Affected products and versions

- Red Hat / Red Hat Enterprise Linux 10 (libssh): ≥ 0:0.12.0-3.el10_2; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Hardened Images (libssh-main): ≥ 0.12.1-4.hum1; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (libssh): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (libssh): Version range not reported. Source: CNA: redhat

## NVD configuration conditions

Affected CPE matches depend on the following AND/OR and negation conditions:

```json
[
  {
    "negate": false,
    "nodes": [
      {
        "cpeMatch": [
          {
            "criteria": "cpe:2.3:a:libssh:libssh:-:*:*:*:*:*:*:*",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:a:redhat:hardened_images:-:*:*:*:*:*:*:*",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:redhat:enterprise_linux:10.0:*:*:*:*:*:*:*",
            "vulnerable": true
          }
        ],
        "negate": false,
        "operator": "OR"
      }
    ],
    "operator": "OR"
  }
]
```

## Severity and prioritization

- CVSS 3.1: 8.8 (high); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H; source: CNA: redhat

- CVSS 3.1: 8.8 (high); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H; source: NVD: secalert@redhat.com

- CISA KEV: No listing in collected sources

- EPSS: 0.49% as of 2026-11-04; percentile 42.24%

- SSVC: exploitation none; automatable no; technical impact total; source ADP: CISA-ADP

- Weaknesses: CWE-863

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://access.redhat.com/errata/RHSA-2026:42922 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:55855 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/security/cve/CVE-2026-59851 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2498184 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:42922 (secalert@redhat.com; Issue Tracking)

- https://access.redhat.com/errata/RHSA-2026:55855 (secalert@redhat.com)

- https://access.redhat.com/security/cve/CVE-2026-59851 (secalert@redhat.com; Vendor Advisory)

- https://bugzilla.redhat.com/show_bug.cgi?id=2498184 (secalert@redhat.com; Issue Tracking, Vendor Advisory)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-59851; retrieved 2026-11-05; source updated 2026-11-04

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-59851; retrieved 2026-11-05; source updated 2026-11-04

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-59851; retrieved 2026-11-05; source updated Not reported

Revision: 4cfac0ea9450e89ec48e896e2734bdf7778d33a9e595a4a2c312f95934b61728

Canonical: https://y2.dev/cve/CVE-2026-59851

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